1. Field of the Invention
This invention generally relates to computer-implemented methods, computer-readable media, and systems for determining one or more characteristics of a wafer.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Metrology processes are performed at various steps during a semiconductor manufacturing process to monitor and control the process. Metrology processes are used to measure characteristics of wafers that generally cannot be determined using inspection tools. There are, however, a number of disadvantages to using metrology processes and tools for process monitoring and control applications. For example, most metrology tools are relatively slow. Therefore, metrology processes are often performed at one location or a limited number of locations on wafers. However, metrology characteristic(s) can vary across the surface of the wafers. As such, metrology measurements performed at one location or a limited number of locations on a wafer may not provide sufficient information about the characteristic(s) of the wafers such that processes can be accurately monitored and controlled. Furthermore, using metrology tools to measure characteristics across the wafer for inline monitoring and control applications is not feasible. In particular, metrology measurements performed by currently available metrology tools are not suitable for high sampling of wafers for inline monitoring since the measurements will impact cycle time in production.
Attempts have been made to try to use inspection systems to determine metrology-like characteristics of wafers. For example, typically, inspection systems are configured with a number of collectors or channels. Each of these collectors or channels is able to capture multiple characteristics of the inspection surface. In the above described method, surface anomalies or features are extracted and then compared with similar features from separate signals. Therefore, currently used detection methods disadvantageously have to discriminate against common background and nuisance features to extract the surface anomalies or features of interest.
Accordingly, it would be advantageous to suppress background and nuisance surface features in output generated by an inspection system for a wafer before the output is used to determine one or more characteristics of the wafer.